Toward pursuing high‐performance photodetectors based on 2D transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2), it is desirable to reduce the high dark current and sluggish response time. Here, in multilayer MoS2‐based photodetectors, a 2D halide perovskite, (C6H5C2H4NH3)2PbI4 ((PEA)2PbI4), is introduced as a bifunctional material: both as electron reservoir to reduce free carriers and passivation agent to passivate defects. Surprisingly, dark current is suppressed by six orders of magnitude after coating a (PEA)2PbI4 thin layer onto pristine MoS2 photodetector, with the dark current decreased to 10−11 A. This huge reduction of dark current suggests an efficient interlayer charge transfer from MoS2 to (PEA)2PbI4, which is further verified by photoluminescence quenching phenomenon. It indicates that (PEA)2PbI4 serves as electron reservoir to reduce carrier density of MoS2, resulting in ultrahigh detectivity (1.06 × 1013 Jones). Moreover, the response speed is also accelerated by more than 100‐fold due to passivation by 2D perovskite. In addition, it is found that this type of photodetectors can further work at self‐power mode (with the bias of 0 V). Therefore, the strategy of applying 2D perovskite on the surface of TMDs provides a novel way to fabricate high‐performance photodetectors.

The electron transport layer (ETL) plays an important role in determining the device performance of perovskite solar cells (PSCs). Recently, SnO2 has been used extensively as an ETL due to its many outstanding optoelectronic properties. Herein, we develop Ta doped SnO2 (Ta-SnO2) as an ETL grown by chemical bath deposition, allowing the fabrication of low-temperature PSCs. In contrast to pristine SnO2, the I-V curve and transmittance spectra show a significant conductivity improvement of Ta-SnO2 without declining the light transmittance property. Meanwhile, Ta-doping could accelerate the electron transfer and decrease the recombination probability at the SnO2/perovskite interface, as well as passivate the electron traps, leading to the improvement in the PSC performance. Through a series of optimization methods, the champion device shows a power conversion efficiency of 20.80%, with an open-circuit voltage of 1.161 V, a short-circuit current density of 22.79 mA/cm2, and a fill factor of 0.786. SnO2 with a suitable Ta content is a promising candidate as an ETL for fabricating high-efficiency PSCs via the low-temperature process.

With the capability to manipulate the built‐in field in solar cells, ferroelectricity is found to be a promising attribute for harvesting solar energy in solar cell devices by influencing associated device parameters. Researchers have devoted themselves to the exploration of ferroelectric materials that simultaneously possess strong light absorption and good electric transport properties for a long time. Here, it is presented a novel and facile approach of combining state‐of‐art light absorption and electric transport properties with ferroelectricity by the incorporation of room temperature 1D ferroelectric perovskite with 3D organic–inorganic hybrid perovskite (OIHP). The 1D/3D mixed OIHP films are found to exhibit evident ferroelectric properties. It is notable that the poling of the 1D/3D mixed ferroelectric OIHP solar cell can increase the average Voc can be increased from 1.13 to 1.16 V, the average PCE from 20.7% to 21.5%. A maximum power conversion efficiency of 22.7%, along with an enhanced fill factor of over 80% and open‐circuit voltage of 1.19 V, can be achieved in the champion device. The enhancement is by virtue of reduced surface recombination by ferroelectricity‐induced modification of the built‐in field. The maximum power point tracking measurement substantiates the retention of ferroelectric‐polarization during the continued operation.

A facile acetic acid modification is introduced to passivate the defects at the SnO2/perovskite interface, thus improving the device performance.

Quasi-2D perovskites have attracted extensive attention due to their extraordinary stability compared to their 3D counterparts. Presently, the bottleneck in quasi-2D perovskite solar cells is their relatively low efficiency. The intrinsic interior carrier transport in the perovskite layer consisting of disorderly oriented phases and inadequate optimization of interfacial carrier transfer have greatly limited the overall device performance. A comprehensive study on effective phase manipulation in the BA2MA4Pb5I16 (n = 5) quasi-2D perovskites is presented to pursue optimal efficiency. With the assistance of the solvent DMSO in a constant thermal-annealing spin-coating (CTAS) process, the crystalline growth process in the quasi-2D perovskite film is effectively manipulated and delicate energy band alignment by eliminating the n ≤ 2 phases at the bottom surface has been successfully achieved. Consequently, a significant improvement of carrier transport in the perovskite layer and photogenerated hole extraction at the interface has been accomplished. The champion device exhibited a boosted PCE of 17.66%.

Two-dimensional (2D) perovskite materials are a promising platform to construct high performance photodetectors due to their novel structure, high stability, resistance to ion migration and decent light harvesting ability.

It is essential to release annealing induced strain during the crystallization process to realize efficient and stable perovskite solar cells (PSCs), which does not seem achievable using the conventional annealing process. Here we report a novel and facile thermal gradient assisted crystallization strategy by simply introducing a slant angle between the preheated hot plate and the substrate. A distinct crystallization sequence resulted along the in-plane direction pointing from the hot side to the cool side, which effectively reduced the crystallization rate, controlled the perovskite grain growth, and released the in-plane tensile strain. Moreover, this strategy enabled uniform strain distribution in the vertical direction and assisted in reducing the defects and aligning the energy bands. The corresponding device demonstrated champion power conversion efficiencies (PCEs) of 23.70% and 21.04% on the rigid and flexible substrates, respectively. These highly stable rigid devices retained 97% of the initial PCE after 1097 h of storage and more than 80% of the initial PCE after 1000 h of continuous operation at the maximum power point. This novel strategy opens a simple and effective avenue to improve the quality of perovskite films and photovoltaic devices via strain modulation and defect passivation.

No abstract